The present invention relates to control valves and, more particularly, relates to a double valve having a cross exhaust capable of replacing two separate valves.
Machine tools of various types operate through a valving system, which interacts with a pneumatically controlled clutch and/or brake assembly. For safety reasons, the control valves that are used to operate these machine tools require the operator to actuate two separate control signal applying contacts essentially simultaneously. This requirement of simultaneous application ensures that the operator will not have his hand near the, moving components of the machine tool when an operating cycle is initiated. The two-control signal applying contacts can then be connected to the valving system that allows compressed air to be delivered to the machine tool to perform its operating cycle.
Safety rules and regulations require the valving system to be designed such that if a component in the valving system malfunctions, the valving system will not allow additional movement of the machine tool. In addition, the valving system must ensure that a new operation cycle of the machine tool cannot be initiated after a component of the valving system has become defective.
Prior art electromagnetic valving systems, which are utilized for the operation of machine tools, meet these safety requirements through the use of a double valve assembly. The double valve assembly includes two electromagnetic supply valves that are normally closed. Each of the supply valves is moved to an open position in response to an electrical control signal. The two supply valves are arranged in series with respect to the source of compressed air.
The double valve assembly also includes two exhaust valves, which are normally open. Each exhaust valve is closed by a respective supply valve when it is opened. It is therefore necessary for the supply valves to be opened simultaneously, otherwise supply air will be exhausted from the system through one of the exhaust valves. The opening and closing of the valve units is monitored by sensing air pressures in the respective valve units and then comparing these two pressures. The monitoring and comparing of these two pressures are accomplished by using a single air cylinder that is separated into two chambers by a piston. The pressure in each valve unit is delivered to one of the chambers. Thus, unequal pressures in the valve units will cause movement of the normally static piston, which will then interrupt the electrical signal to one of the valve units. This and other external electronic monitoring arrangements are expensive and require that electrical signal processing equipment be designed and utilized.
The continued development of the valving systems for machine tools has been directed toward more reliable, simpler, and less costly valving systems that both meet and exceed the safety performance requirements in force today as well as those proposed for the future.
According to the principles of the present invention, a control valve system is provided that includes a housing defining a first inlet, a second inlet, a first outlet, a second outlet, and an exhaust to define an intrinsically safe double valve. The double control valve system of the present invention further includes a pair of cross exhaust passages that eliminates the need for complicated timing devices.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.